The subject matter disclosed herein relates to motion control systems and, more specifically, to a method and apparatus for coordinating motion of external devices with the motion of multiple independent movers traveling along a track in a linear drive system.
Motion control systems utilizing movers and linear motors can be used in a wide variety of processes (e.g. packaging, manufacturing, and machining) and can provide an advantage over conventional conveyor belt systems with enhanced flexibility, extremely high speed movement, and mechanical simplicity. The motion control system includes a set of independently controlled “movers” each supported on a track for motion along the track. The track is made up of a number of track segments that, in turn, hold individually controllable electric coils. Successive activation of the coils establishes a moving electromagnetic field that interacts with the movers and causes the mover to travel along the track. Sensors may be spaced at fixed positions along the track and/or on the movers to provide information about the position and speed of the movers.
Each of the movers may be independently moved and positioned along the track in response to the moving electromagnetic field generated by the coils. In a typical system, the track forms a closed path over which each mover repeatedly travels. At certain positions along the track other actuators may interact with each mover. For example, the mover may be stopped at a loading station at which a first actuator places a product on the mover. The mover may then be moved along a process segment of the track where various other actuators may fill, machine, position, or otherwise interact with the product on the mover. The mover may be programmed to stop at various locations or to move at a controlled speed past each of the other actuators. After the various processes are performed, the mover may pass or stop at an unloading station at which the product is removed from the mover. The mover then completes a cycle along the closed path by returning to the loading station to receive another unit of the product.
Traditionally, the location of a mover along the track is determined with respect to a linear position along the track. For a closed track, that is a track where “the end” of the track joins “the start” of the track such that a mover will repeatedly travel the length of the track when traveling in a single direction, the start of the track may be assigned a position, such as zero, which establishes a reference position. As the mover travels along the track, whether in a straight or curved path, the position along the track increases until the mover reaches the end of the track. When the mover transitions from the end back to the start, the position of the mover is reset to the initial, or reference, position. Thus, a single coordinate may be used to define a location of each mover along the track.
The single coordinate system is suitable for defining the location of movers along the track when a central controller need only coordinate the position of each mover with respect to the other movers. However, in certain applications, it may be desirable for an external device to engage or interact with a load present on the mover as the mover travels along the track. In order for the external device to interact with the mover, the motion of the mover must be coordinated with the motion of the external device.
Historically, coordination of motion between the external device and a mover has been limited. For example, the external device may be configured to travel in parallel to the mover. A sensor, position feedback information for the mover, or the like may indicate when the mover reaches a start position. A system controller may use the sensor or position feedback information to initiate travel of the external device in tandem with the mover. The external device may be, for example, a fill mechanism that dispenses product into a container on the mover as the mover travels. When a second sensor or subsequent position feedback information indicates the mover has reached an end position, the system controller may indicate to the external device to stop filling the container and return to the start position. This manner of motion coordination between a mover and an external device is, however, limited in the applications that may be performed to those that can match the linear travel of the mover.
Thus, it would be desirable to provide an improved system and method for coordinating motion between an external device and independent movers traveling along a linear drive system.